Galvanised iron (GI) has long been used to make delivery pipes for carrying water from submersible pumps. Pipe systems that deliver water from deep bore wells are designed so that the system, which essentially comprises pipes and joints, should:                Withstand the submersible pump's dead weight, the pressure developed by the pump, the reverse thrust created by the upward flow of water, and the water hammer effect created by the start/stop operations of the pump.        Withstand the torque developed by the start/stop operations of the pump        Be corrosion resistant        Be easy to install and dismantle in field        Minimize the friction losses        Be cost effective.        
The conventional GI pipes normally satisfy the first two stress-related requirements, that is, that of withstanding the various forces and stresses applied to them. However, all GI pipes, including steel ones, are susceptible to chemical corrosion. Various factors such as pH, and levels of dissolved oxygen (DO), hydrogen sulphide, total dissolved solids, CO2, dissolved iron, and dissolved manganese, contribute to chemical corrosion of GI pipes. Galvanic corrosion in galvanized pipes, which are bi-metal in constitution, is caused by high level of total dissolved solids in water.
Steel pipes are typically of high specific gravity. This makes the pipes and related accessories and also the handling equipment heavy, which ultimately makes it difficult to handle and also expensive.
Another disadvantage of the GI pipes is that the pipe system requires special sealants in the form of chemicals or Teflon tape in order to make joints in the system leak-proof.
A further disadvantage of the GI pipes is that their inner surface is rough which leads to greater friction losses. During the life of the GI pipes, the inside surface gets pitted or deposited with carbonates, thereby leading to an increase in the friction losses in the pipe, ultimately resulting in reduced discharge.
The pitting of the inside surface of the GI pipes also necessitates their frequent replacement increasing the maintenance cost of the system.
A further disadvantage resulting from the friction losses is that the pumps have to operate at higher dynamic head, which reduces the effective life of the pump and increases the energy consumption.
There have been attempts to provide a PVC pipe-based system in an effort to eliminate the various drawbacks and disadvantages of the GI pipe system. Systems made from plastic are available, however these systems are normally not able to satisfactorily withstand the forces and stresses put on them under the field conditions, more specifically the stresses generated due to the submersible pump's dead weight, the pressure developed by the pump, the reverse thrust created by the upward flow of water, and the water hammer effect created by the start/stop operations of the pump, and the torque developed by the start/stop operations of the pump.
Some attempts have been made to resolve this problem by developing joints made from pipes that have special threads. However their drawback is that although they are able to withstand the unidirectional torque, under the bi-directional torque or the torque that changes direction, they are not effective and the joints do not remain locked. Moreover, the threads of the plastic joints wear out more quickly than metal threads during the maintenance or repair operations.
There have been attempts to resolve the problem of joint unlocking by providing metallic wires in the threaded joints. The approach here has been to resolve the problem of joints unlocking under the bi-directional torque conditions. The factory fitted joints do resist the bidirectional torque; however, the field-fitted joints loosen under the field conditions. Moreover, even here the problem of thread wear-out persists.
Pipe joint systems that eliminated threads are available. In one such system, grooves and locking screws are provided. Grooves are provided on the OD of the pipe and ID of the coupler. This forms a passage through which spline intended for resisting tensile stresses is placed. Screws are provided for torque resistance. However, the drawback of these joints is that the screws loosen under the field operating conditions. This leads to rotation of pipes inside the coupler resulting in winding of the cable around the pipe and finally breakage of the cable. Also, it is found that the screws tend to damage the pipes themselves.
There is therefore a need to provide a system of joints that will withstand the stresses and forces imposed on a pipe system carrying fluids during field conditions.